In actual fire, a solid wall is commonly established using nearby noncombustible solid materials to resist flame propagation. However, there are always some narrow channels owing to uneven surface of solid materials. There are inherent differences between liquid flame spread in narrow channels and infinite width fuel, including dynamic shear and heat dissipation. The experiments of flame spread over n-butanol fuel in narrow channels with lengths of 30, 50, 100, 200 and 300 mm and widths of 3, 4, 5, 6, 7, 8, 9 and 10 mm are carried out. The flame spread is divided into initial stage, restriction stage and jet flow stage. The velocity of subsurface flow decreases strongly once the convective flow enters narrow channel. Based on the assumption that surface tension is balanced with sum of viscous force and shear force, the velocity of subsurface flow at restriction stage is calculated which overestimates similar to 10% of measurement. The flame cannot pass through the channel when heat loss accounts for more than 43% of total heat flux of subsurface flow. The heat absorption by sidewalls always accounts for more than 80% of total heat loss. The current finding provides a theoretical guidance for actual liquid firefighting.